"If we don't get the right agreement internationally for the period after which the Kyoto protocol will expire - that's in 2012 - if we don't do that then I think we are in serious trouble," he told a parliamentary committee.

Asked if the world had seven years to implement measures on climate change before the problem reached "tipping point", Blair answered: "Yes".

The European Union, Japan and much of the rest of the industrialised world are imposing mandatory cuts on emissions of heat-trapping gases from burning fossil fuels under Kyoto.

US President George W Bush pulled out of Kyoto in 2001, arguing it would hurt the American economy and that developing countries were exempted. He favours asking US companies to join a voluntary emission reduction programme.

Blair said targets were key to any successor to Kyoto.

"This can only be done if you have a framework that, in the end, has targets within it. If you don't get to that point, the danger is you never have the right incentives for the private sector to invest heavily in green technology," he said. Environment ministers in Montreal in December agreed on a road map to extend Kyoto and to hold talks to include the United States and developing countries in a future framework.

Blair said there were the "beginnings" of an international consensus and that Bush's comment in his State of the Union speech last week that America was "addicted to oil" was a sign of a change of mood but he urged Bush to move further.

"I think there are real signs of change," he said. "I think if you could find a way of ensuring the right incentives were given without America feeling there was some desire to inhibit its economic growth, then I think we can find a way through."

Blair also said he thought it was unrealistic to hope for an international agreement on restricting aviation travel to curb pollution and he dismissed the idea of Britain unilaterally or bilaterally slapping a tax on commercial flights.